This invention relates to a process for preparing ketone compounds and the products obtained by this process. More particularly, the invention relates to the preparation of intermediate compounds in the manufacture of pesticides.
Pesticidal 4-benzoylisoxazoles, particularly 5-cyclopropylisoxazole herbicides and intermediate compounds in their synthesis, are described in the literature, for example in European Patent Publication Nos. 0418175, 0487357, 0527036, 0560482, 0609798 and 0682659.
Various methods for preparing these compounds are known. It is an object of the present invention to provide improved methods for the preparation of these compounds and the intermediate compounds thereto.
According to a first aspect of the invention, there is provided a process for the preparation of a compound of formula (I) by the reaction of a compound of formula (II) with a compound of formula (III), according to the reaction scheme Sc1 indicated below: 
wherein:
R1 is lower alkyl;
R2 is lower alkyl; or phenyl optionally substituted by from one to five groups which may be the same or different selected from lower alkyl, lower haloalkyl, halogen and xe2x80x94SR4;
R3 is halogen, lower alkyl, lower haloalkyl, lower alkoxy, lower haloalkoxy, xe2x80x94S-alkyl, cycloalkyl having from 3 to 7 ring carbon atoms, alkenyl or alkynyl having from 3 to 7 carbon atoms, or xe2x80x94(CR5R6)qxe2x80x94SR2 wherein q is one or two;
n is zero or an integer from one to three;
R4 is lower alkyl;
and R5 and R6 independently represent hydrogen, lower alkyl or lower haloalkyl.
According to a second aspect of the present invention, there is provided a process for the preparation of a compound of formula (II) by the reaction of a compound of formula (V) with a mercaptan of formula (IV), optionally present in the form of the thiolate, according to reaction scheme Sc2 indicated below: 
wherein R2, R3 and n in formulae (II) and (V) have the same meanings as given before in reaction scheme Sc1. The group xe2x80x94NO2 is generally present in the 2- or 4-position, preferably the 2-position of the phenyl ring.
According to a third aspect of the invention there is provided a process for the preparation of a compound of formula (V) by the reaction of a compound of formula (VII) or (VI), as well as a process for the preparation of a compound of formula (VI) from a compound of formula (VII), according to the reaction scheme Sc3 indicated below: 
wherein R3 and n have the same meanings as in reaction schemes Sc2 and Sc1, and X represents halogen, preferably chlorine or fluorine. Preferably, the group xe2x80x94NO2 in formula (VII) is in the 2- or 4-position, most preferably in the 2-position of the phenyl ring.
Certain intermediate compounds of formula (II) are novel and as such constitute a further feature of the present invention, in particular 2-methylthio-4-trifluoromethylacetophenone and 3,4-dichloro-2-(methylthio)acetophenone.
The compounds of formula (I) and a number of processes for their preparation have been described in the European Patent Applications cited above.
By the term xe2x80x9clowerxe2x80x9d is meant radicals comprising at least one hydrocarbon chain, it being understood that such radicals contain from one to six carbon atoms linked together in a straight- or branched-carbon chain.
Preferably, R1 and R2 are lower alkyl (most preferably, methyl).
Preferably, the group xe2x80x94SR2 occupies the 2-, 3- or 4-position of the phenyl ring (most preferably, the 2-position).
Preferably, n is one or two.
The reaction generally proceeds in better yield when a group R3 is not halogen in the 2-position of the phenyl ring.
Preferably, R3 is halogen or trifluoromethyl. More preferably, (R3)n is 4-CF3 or 3,4-dichloro.
The compounds of formula (III) above used in Scheme Sc1 are known in the literature and their preparation has been expressly described in the prior art known to the skilled worker. Some references particularly pertinent to the preparation of this reagent may be found by the skilled worker in various sources of chemical literature, including Chemical Abstracts and information databases available to the public.
The preparation of compounds of formula (I) using compounds of formula (II) and (III) according to scheme Sc1 above may be preferably effected in a polar or apolar aprotic solvent. Examples of polar aproptic solvents include dimethylsulfoxide, dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, a compound of formula (III); an ether compound, particularly dioxane and tetrahydrofuran; or an aromatic or aliphatic halogenated hydrocarbon, particularly chlorobenzenes. Examples of apolar aprotic solvents include aromatic or aliphatic hydrocarbons, particularly toluene and xylenes.
Generally, the reaction temperature used in Sc1 above is from 0xc2x0 C. to the boiling point of the solvent, preferably, between 0xc2x0 C. and 100xc2x0 C. Generally the Sc1 reaction takes place in the presence of a strong base, which is most preferably selected from an alkoxide of an alkali or alkaline earth metal, notably sodium ethoxide, sodium methoxide, sodium or potassium t-butoxide; and a metal hydride (notably sodium hydride).
According to a preferred variant of the process of Sc1 of the present invention, the reaction is performed with continuous distillation of the alcohol R1xe2x80x94OH formed in the course of the reaction, at atmospheric pressure or under reduced pressure (preferably from 1 to 20% below atmospheric pressure). Optionally, the alcohol R1xe2x80x94OH formed may be removed by the use of a suitable molecular sieve, for example a 4 Angstrom molecular sieve.
Compounds of formula HSR2 used in reaction scheme Sc2 are known in the literature and their preparations are expressly described in the prior art known to the skilled worker. The references particularly pertinent to the preparation of this reagent may be found by the skilled worker in various sources of classical chemistry including Chemical Abstracts and information databases available to the public. The salts or thiolates derived from the compound of formula (IV) may be prepared by means known to the skilled worker. These thiolates are preferably alkaline salts, particularly sodium or potassium thiolate.
The preparation of compounds of formula (II) according to scheme Sc2 from the acetophenone of formula (V) and a compound of formula (IV) is preferably performed in a solvent of the compound of formula (IV) which may be inert to the reaction conditions. Examples of other suitable solvents include sulfoxides such as dimethylsulfoxide; amides such as dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone; ketones such as acetone and methyl isobutyl ketone; ether solvents, particularly dioxane and tetrahydrofuran; aromatic, aliphatic and cycloaliphatic hydrocarbons and halogenated or non-halogenated hydrocarbons, particularly chlorobenzene, dichloromethane and toluene. The presence of a small quantity of water is also acceptable in allowing the solubilization of the thiolate.
When the reaction according to scheme Sc2 takes place using a compound of formula (IV) in the form of the mercaptan and not in the form of a thiolate salt, the reaction is preferably effected in the presence of a base such as a hydroxide of an alkali metal or alkali earth metal (preferably, sodium or potassium), or a carbonate or hydride (such as sodium hydride). The reaction may also be performed using various forms of catalyst, particularly phase transfer catalysts such as a quaternary ammonium salt, for example, tetrabutylammonium bromide.
The two reactions which comprise together the reaction scheme Sc3 above are generally distinct but preferably they may occur in succession. That is, the compounds of formula (V) may be prepared from the compounds of formula (VII) via an intermediate of formula (VI) which may be isolated or used in situ in the course of the reaction.
The reaction conditions for the preparation of the compound of formula (V) from the compound of formula (VI) are known in the art and described in the literature, notably by J. G. Reid and J. M. Reny Runge in Tetrahedron Letters, Vol. 31(1990), pp. 1093-1096; G. A. Olah et al. Synthesis (1980), pp. 662-663; N. Kornblum et al, J. Org. Chem., Vol. 47 (1982), pp. 4534-38; S. Chandrasekaran et al, Synthetic Communications, Vol. 17 (1987), pp. 195-201.
The invention is thus also concerned with the preparation of compounds of formula (VI) from compounds of formula (VII) by the reaction of nitroethane in the presence of a base in a solvent which is selected from a compound of formula (VII), nitroethane, a solvent inert to the reaction conditions, and the base being selected from an hydroxide, a carbonate, a hydride, an alkoxide of an alkaline metal or an alkaline earth metal, and guanidine. An advantage of this aspect of the present invention is that relatively simple bases may be used in the reaction scheme Sc3.
Solvents suitable for use in preparing compounds (VI) from compounds (VII) include nitroethane itself (used in excess compared to the quantity normally used as a reactant); aromatic or aliphatic halogenated or non-halogenated hydrocarbons, particularly chlorobenzene; aromatic or aliphatic hydrocarbons, particularly toluene and xylenes; polar aproptic solvents such as dimethylsulfoxide, dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone; acetonitrile; ether solvents, particularly dioxane and tetrahydrofuran. The presence of a small quantity of water is also acceptable in allowing the solubilization of the reaction mixture, while not reacting with the reactants themselves.
The reaction temperature for converting (VII) to (VI) is generally from 0xc2x0 C. to 50xc2x0 C. The reaction may also be carried out in an aqueous or non-aqueous medium. Among the bases suitable for the use in this process, one may cite hydroxides or carbonates of alkali metals or alkaline earth metals, preferably sodium or potassium, sodium carbonate, potassium carbonate or cesium carbonate; or tetramethylguanidine. These bases may be used alone or in mixture with others. The reaction may also be conveniently performed using various types of catalyst, particularly phase transfer catalysts such as a quaternary ammonium salt, for example, tetrabutylammonium bromide.
The following non-limiting examples illustrate the invention.